Fork Down tube air leak?

[TomE]

Something does not add up. I can set my air compressor to 30 PSI, fill the forks through the Schrader valve, take the air chuck off and immediately put an air pressure gauge on, and the gauge will show 0 PSI.

I don't hear any air leaks while the air chuck is attached. I don't feel air blowing when I move my hand around the air hoses. I have tried this with the little air stop valves open and closed.

I do hear a very small ffft sound when I take the air chuck off. Very short and small. But when I press the valve stem again, nothing. It's empty.

I don't see any oil leaks from the fork oil seals, for what that's worth.

Any idea what's up?

It's a 1981 GS1100E.

[BassCliff]

Hi,

A few thoughts, if I may.

30 psi in your forks is quite a lot. Before I got progressive springs I would run 15 psi and that was plenty stiff. I use no air preload now.

I would suspect your fork seals are leaking the air. Or perhaps the crossover air hose that goes between the forks. I had to fill my forks individually, no crossover.

Are there O-rings at the top of the forks where the caps screw in? How do those look?


Thank you for your indulgence,

BassCliff

[TomE]

Hi BassCliff,

Thanks for the response. Yes, 30 PSI is a lot, I agree. But seeing as the bike is on a lift right now, it's at least under the 35 PSI the book says is the limit.

I have o-rings at the fork cap, two sets around the lower clamp, where the crossover hose is, two o-rings at the air stop lock screws.

These stop screws seem to isolate each tube from the other and from the Schrader valve and crossover system when shut. I think they need to be open to fill the tubes.

I don't really want to tear it all apart to change something that "might" be leaking. The idea of using progressive springs and no air preload is becoming attractive!

I think I will take the fork caps off tonight and see what I can see.

Tom

[twr1776]

Today 04:16 PM TomE The idea of using progressive springs and no air preload is becoming attractive!

+ 1, I agree with Cliff and would definately recommend going to the the Progressive/No Air system, it is worth every penny. Cliffs site has a good tutorial on how to do it.

A mandatory safety upgrade IMHO.

[tejasmud]

I did a Progressive change as well on my bike. It seems to be one of the desired solutions to eliminate the air all together. It actually sits up now with no air.

But, if you are content with using air to preload.

I would check the Schrader valve plug and seat to make sure it is working. Has it had the cap on it? If not it could be stuck, dirty, or just worn out.

But, if the valve is all good, pressure up the forks and spray the fork seals/dust boots, plugs/caps at the top of the forks, and the crossover/stop screws with some soapy water. It should show where the leak(s) are coming from.

Yes, the stop screws isolate each fork leg, and need to be open to fill I think. Unless they are like back check valves, but from the schematic they look like simple needles with o-rings. Unsure how far they need to be backed out to allow fill..

E

[hikermikem]

Assuming everything is tight & holding air, that quick pffft sound you hear when removing the fill fitting is most likely reducing & eliminating your fork pressure... I know when i do it I have to make an effort to remove that fitting as straight & quick as possible to minimize air leakage. It desn't appear there's too much volume to start with so it doesn't take long to purge it.

I also agree that 30 psi is on the very high side of what these old forks will tolerate. I usually hit mine with 20-25 psi & use the "pressure release" button on the pressure gage to slowly wean out the pressure on each fork to around 10 psi...

[oldgrumpy]

upgrading front end ..... gs1000e

i have a 1980 gs1000e,,, with air over ... in its old life...i took a few guys good advice and fitted brand new progressive springs from USA ... new 10wt fork oil and I DO NOT USE AIR AT ALL... the bike also has a gsx1100 alloy swing arm and new tires,,, it handles like a treat,,,, i cann,t wipe the grin from my face .... when riding... hope this helps regards david

[TomE]

So chuck the air pressure and go to Progressive springs. Huuh. That's the setup I have in my '75 Goldwing and it works very well.

I think I see a set of springs in my future. That would sure be easier than tearing apart the whole front end of the GS looking for an air leak! And that would match the Progressive shocks the PO put on the back.

[gs road racer]

Here's a site I posted before all about suspension setup....great info good read

http://www.bikesetup.com/

Randy

[TomE]

Nice site, Randy, I have spent some time there and will spend some more. Lots of food for thought.

[Big T]

Tom,

Never use a compressor on your forks. That's a sledgehammer approach

The proper tool is a hand pump with a hose. It looks like a veternary syringe. You only want 8-10 psi in there and there's not much volume